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Date: Mon, 28 May 2012 18:49:14 +0200
From: Richard Cochran <richardcochran@...il.com>
To: linux-kernel@...r.kernel.org
Cc: John Stultz <john.stultz@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RFC V1 5/5] timekeeping: Use a continuous timescale to
tell time.
On Fri, Apr 27, 2012 at 10:12:44AM +0200, Richard Cochran wrote:
> This patch converts the core time keeping code to use a continuous
> timescale called the Kernel Time Scale (KTS). KTS is based on the
> TAI timescale but can be offset from it by an integral number of seconds.
> Every function that returns UTC time now coverts the seconds by adding
> the current KTS - UTC offset.
>
> As a result of this change, the NTP leap second code is considerably
> simplified and hopefully more robust.
>
> Signed-off-by: Richard Cochran <richardcochran@...il.com>
> ---
> include/linux/timex.h | 2 +-
> kernel/time/ntp.c | 81 ++++++++++----------------------------------
> kernel/time/timekeeping.c | 73 ++++++++++++++++++++++++++++++++--------
> 3 files changed, 79 insertions(+), 77 deletions(-)
>
> diff --git a/include/linux/timex.h b/include/linux/timex.h
> index 99bc88b..9461e6f 100644
> --- a/include/linux/timex.h
> +++ b/include/linux/timex.h
> @@ -252,7 +252,7 @@ extern void ntp_clear(void);
> /* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
> extern u64 ntp_tick_length(void);
>
> -extern int second_overflow(unsigned long secs);
> +void second_overflow(void);
> extern int do_adjtimex(struct timex *);
> extern void hardpps(const struct timespec *, const struct timespec *);
>
> diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
> index d0a2183..91de2f8 100644
> --- a/kernel/time/ntp.c
> +++ b/kernel/time/ntp.c
> @@ -16,6 +16,7 @@
> #include <linux/mm.h>
> #include <linux/module.h>
>
> +#include "leap-seconds.h"
> #include "tick-internal.h"
>
> /*
> @@ -24,6 +25,7 @@
>
> DEFINE_SPINLOCK(ntp_lock);
>
> +#define STA_LEAP (STA_INS | STA_DEL)
>
> /* USER_HZ period (usecs): */
> unsigned long tick_usec = TICK_USEC;
> @@ -42,19 +44,9 @@ static u64 tick_length_base;
> * phase-lock loop variables
> */
>
> -/*
> - * clock synchronization status
> - *
> - * (TIME_ERROR prevents overwriting the CMOS clock)
> - */
> -static int time_state = TIME_OK;
> -
> /* clock status bits: */
> static int time_status = STA_UNSYNC;
>
> -/* TAI offset (secs): */
> -static long time_tai;
> -
> /* time adjustment (nsecs): */
> static s64 time_offset;
>
> @@ -386,57 +378,14 @@ u64 ntp_tick_length(void)
> * They were originally developed for SUN and DEC kernels.
> * All the kudos should go to Dave for this stuff.
> *
> - * Also handles leap second processing, and returns leap offset
> */
> -int second_overflow(unsigned long secs)
> +void second_overflow(void)
> {
> s64 delta;
> - int leap = 0;
> unsigned long flags;
>
> spin_lock_irqsave(&ntp_lock, flags);
>
> - /*
> - * Leap second processing. If in leap-insert state at the end of the
> - * day, the system clock is set back one second; if in leap-delete
> - * state, the system clock is set ahead one second.
> - */
> - switch (time_state) {
> - case TIME_OK:
> - if (time_status & STA_INS)
> - time_state = TIME_INS;
> - else if (time_status & STA_DEL)
> - time_state = TIME_DEL;
> - break;
> - case TIME_INS:
> - if (secs % 86400 == 0) {
> - leap = -1;
> - time_state = TIME_OOP;
> - printk(KERN_NOTICE
> - "Clock: inserting leap second 23:59:60 UTC\n");
> - }
> - break;
> - case TIME_DEL:
> - if ((secs + 1) % 86400 == 0) {
> - leap = 1;
> - time_tai--;
> - time_state = TIME_WAIT;
> - printk(KERN_NOTICE
> - "Clock: deleting leap second 23:59:59 UTC\n");
> - }
> - break;
> - case TIME_OOP:
> - time_tai++;
> - time_state = TIME_WAIT;
> - break;
> -
> - case TIME_WAIT:
> - if (!(time_status & (STA_INS | STA_DEL)))
> - time_state = TIME_OK;
> - break;
> - }
> -
> -
> /* Bump the maxerror field */
> time_maxerror += MAXFREQ / NSEC_PER_USEC;
> if (time_maxerror > NTP_PHASE_LIMIT) {
> @@ -475,8 +424,6 @@ int second_overflow(unsigned long secs)
>
> out:
> spin_unlock_irqrestore(&ntp_lock, flags);
> -
> - return leap;
> }
>
> #ifdef CONFIG_GENERIC_CMOS_UPDATE
> @@ -541,7 +488,6 @@ static inline void notify_cmos_timer(void) { }
> static inline void process_adj_status(struct timex *txc, struct timespec *ts)
> {
> if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
> - time_state = TIME_OK;
> time_status = STA_UNSYNC;
> /* restart PPS frequency calibration */
> pps_reset_freq_interval();
> @@ -554,6 +500,18 @@ static inline void process_adj_status(struct timex *txc, struct timespec *ts)
> if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
> time_reftime = get_seconds();
>
> + /*
> + * Check for new leap second commands.
> + */
> + if (!(time_status & STA_INS) && (txc->status & STA_INS))
> + timekeeper_insert_leap_second();
> +
> + else if (!(time_status & STA_DEL) && (txc->status & STA_DEL))
> + timekeeper_delete_leap_second();
> +
> + else if ((time_status & STA_LEAP) && !(txc->status & STA_LEAP))
> + timekeeper_finish_leap_second();
> +
> /* only set allowed bits */
> time_status &= STA_RONLY;
> time_status |= txc->status & ~STA_RONLY;
Just for the record, this hunk and the following violate the (unspoken
but mentioned in the discussion on V2 series) locking rules for
ntp_lock and timekeerer.lock.
> @@ -597,7 +555,7 @@ static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts
> }
>
> if (txc->modes & ADJ_TAI && txc->constant > 0)
> - time_tai = txc->constant;
> + timekeeper_tai_offset(txc->constant);
>
> if (txc->modes & ADJ_OFFSET)
> ntp_update_offset(txc->offset);
Thanks,
Richard
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